JPS63107898A - Method for synthesizing diamond with plasma - Google Patents

Abstract

PURPOSE:To obtain diamond in the form of a film or a massive crystal having uniform properties or fine powder having a uniform particle size and uniform properties by decomposing or evaporating an org. compd. or a carbonaceous material in plasma and adiabatically expanding the resulting gas. CONSTITUTION:Plasma is generated by electric discharge in a gaseous hydrocarbon, gaseous hydrogen, an inert gas or a gaseous mixture of such gases. An org. compd. or a carbonaceous material is decomposed or evaporated in the plasma and the resulting gas is adiabatically expanded to deposit diamond on a substrate or in a vapor phase. The adiabatic expansion is carried out by introducing the gas in a plasmatic state into a space under lower pressure through a nozzle or an orifice to cause sudden volume expansion. The plasma used may be low temp. plasma generated by glow discharge but hot plasma by which the pressure of the gas and the temp. of the active species are made higher is preferably because it is more effective in adiabatic expansion.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for synthesizing diamond using plasma.

Prior Art Conventionally, the following method is known as a method for synthesizing diamond in a thermodynamically metastable region using electric discharge.

1) Ion beam method or ion brating method in which carbon ions or hydrocarbon ions are created using electric discharge, accelerated by a potential gradient, and collided with the surface of a substrate to deposit diamond.

2) Activated vapor phase deposition method in which a mixed gas of hydrocarbon and hydrogen is activated by low-temperature plasma generated by glow discharge and deposited on the substrate surface.

But 1. Each of these methods has the following drawbacks.

Method 1) has the advantage of being able to deposit a diamond-like carbon film on the substrate surface of various materials at room temperature, but because accelerated ions are used, the deposited diamond has many defects and has poor crystallinity. Diamonds are difficult to obtain,
Furthermore, since the ion beam density cannot be increased, there are drawbacks such as a slow deposition rate.

Method 2) can obtain diamond microcrystals on substrates made of various materials, but since it uses low-temperature plasma caused by glow discharge, plasma will not be generated unless the gas pressure is low, usually 0.3 atmospheres or less. Furthermore, since the concentration of active species such as ions and radicals is as low as about 10% at most, the growth rate of diamond is slow (up to several μm/h 2 ), which is a drawback.

The temperature of the gas (ions, two molecules of atoms) in this low-temperature plasma is about 1600''K or less.

Furthermore, in both methods 1) and 2), diamond could only be obtained on the substrate, and it was impossible to obtain it as a powder in the gas phase.

The applicant has previously proposed using direct current, low frequency, high frequency, and microwave as a method to improve the shortcomings of the conventional method.
By generating high-temperature plasma of 700 K or higher and decomposing or evaporating organic compounds or carbon materials in this plasma, the growth rate of diamond is fast, and it is possible to efficiently grow not only diamond in the form of a film but also in the form of lumps or powder. We have developed a method to synthesize this. (Special application 1986-295
(Refer to No. 739) According to this method, diamond can be obtained at high speed due to high gas pressure and high concentration of active species. It is often necessary to control the temperature of the growth space by spraying. Temperature control by these methods tends to cause non-uniformity in the substrate temperature and growth space temperature, and has the disadvantage that control is difficult.

OBJECT OF THE INVENTION The present invention aims to eliminate this drawback, and its purpose is to easily control the temperature of the substrate and the temperature of the synthesis space to a uniform temperature, thereby producing a film with uniform properties and bulk crystals. Another object of the present invention is to provide a method for obtaining fine powder with uniform particle size and properties.

Structure of the Invention As a result of research to achieve the above object, the present inventor found that by adiabatically expanding a gas obtained in a plasma state, the gas can be uniformly rapidly cooled, and the temperature of the substrate temperature 2 synthesis space can be uniformly controlled. It has been found that the above objective can be achieved. The present invention was completed based on this knowledge.

The gist of the present invention is to generate plasma by electric discharge in a single gas or a mixture of gases selected from hydrocarbon gas, hydrogen gas, and inert gas, and to decompose or evaporate organic compounds or carbon materials in the plasma. This method of synthesizing diamond using plasma is characterized in that diamond is precipitated on a substrate or in a gas phase by adiabatically expanding a gas produced by the plasma.

The adiabatic expansion method is obtained by guiding a plasma-state gas obtained by decomposing or evaporating an organic compound or carbon material in the plasma to a lower pressure space through a nozzle or orifice, and rapidly expanding the volume. .

The plasma used in the method of the present invention may be a low-temperature plasma generated by glow discharge, but a thermal plasma with a high gas pressure and a high active species temperature may have a greater adiabatic expansion effect. Thermal plasma referred to here is a plasma in which the excitation of chemical species in the plasma collides with electrons accelerated by an electric field, and the mechanism resulting from collisions during thermal motion between chemical species is added. The temperature is approximately 1700
K or higher.

Plasma is generated by electrical discharge, and the power source may be direct current, low frequency alternating current, high frequency, or microwave, and either electroded or electrodeless methods may be used. As the plasma generating gas used in the present invention, a hydrocarbon gas, an inert gas such as argon or helium, or hydrogen gas is used alone or as a mixed gas.

When an inert gas or hydrogen gas is used as a plasma generating gas, an organic compound or carbon material is injected into the plasma as a carbon source. The organic compound may be gaseous, liquid, or solid, as long as it can be decomposed in plasma to generate carbon-containing ionic species or radical species. For example, methane, ethane, propane, butane, ethylene.

Hydrocarbons such as benzene, or polyethylene.

It may also be a natural organic compound.

Furthermore, when hydrogen gas is mixed with the plasma generating gas, a carbon source such as carbon monoxide or carbon dioxide may be used. Further, as the carbon material, graphite for electrodes or the like is used.

The pressure of the plasma generating gas can range from 10-4 to 5 x 10" atmospheres. At low pressures, the rate of diamond deposition is slow, and at high pressures, it is difficult to handle the container. The pressure of the deposition chamber is 10" A pressure of -6 to 10 atm is used, but a suitable pressure is 10 -6 to 1 atm to obtain diamond in the form of a film, and 104 to 10 atm to obtain diamond in the form of powder or lumps.Plasma The generation chamber and the precipitation chamber can also be evacuated.

The dimensions of the nozzle or orifice vary depending on the gas flow rate, negative side gas pressure, and secondary side gas pressure, but in the above pressure range, the hole diameter is 0.5 to 20 mm and the large loss is 0.3 to 3 Qmi+.
is appropriate. One or several holes may be used.

In addition, the nozzle or orifice is cooled with water if necessary. Substrates include metals such as molybdenum and stainless steel, semiconductors such as silicon, ceramics such as alumina,
Diamond single crystal etc. are used. Base temperature is 400
~1700°C is desirable. The substrate is heated by the gas emitted from the nozzle or orifice, but if necessary, the temperature can be adjusted using supplementary heating using a heater or the like, or cooling using a refrigerant, gas, or the like.

The apparatus for carrying out the method of the present invention will be explained based on the drawings as shown in FIGS. 1 to 4. FIG. 1 is a schematic diagram of a case where DC discharge is used, FIG. 2 is an AC discharge, FIG. 3 is a high frequency discharge, and FIG. 4 is a schematic diagram using a microwave discharge.

In Fig. 1, 1 is a DC plasma torch, 2 is a DC power source, 3 is a substrate, 4 is a nozzle or orifice, 5 is a plasma generation chamber, 5' is a deposition chamber, 6 is an exhaust device, and 8 to 8' are gas flow rates. The control valve is shown.

The operating procedure is as follows: First, the deposition chamber 5' and the torch section are evacuated by the exhaust device 6, and then predetermined plasma generating gas and organic compound gas are supplied through the valves 8, 8'. After the deposition chamber 5' is brought to a predetermined pressure, power is supplied to the plasma torch 1 from the power source 2 to generate plasma, which is ejected through the nozzle or orifice 4 into the deposition chamber 5'. Base body 3
The position of the holder is adjusted, and diamond is deposited on the substrate 3. Moreover, as shown in FIG. 3, a base body.

It is also possible to remove the substrate holder and synthesize diamond powder in the gas phase.

In FIG. 2, 11 is an electrode for AC discharge, and the lower electrode has a hole in the center and also serves as a nozzle. 12 is an AC power supply, and the others are the same as in FIG. The operating procedure is the same as in the case of direct current discharge, in which plasma gas generated by the discharge between the electrodes is ejected into the deposition chamber 5' through a nozzle or orifice, and diamond is grown on the substrate or in the gas phase.

In this way, in electroded discharge, one electrode can also be used as a nozzle or an orifice.

In Fig. 3, 21 is a high-frequency plasma torch, 22 is a high-frequency power source, 23 is a work coil, 24 is a solid-liquid raw material introduction device, 25 is a tray for receiving the produced diamond powder, and the other parts are the same as in Fig. 1. . Plasma can also be generated by capacitive coupling using electrodes instead of the work coil 23. In this case as well, the generated plasma gas is ejected into the precipitation chamber 5' through a nozzle or orifice to generate fine diamond powder. Furthermore, by placing the substrate as shown in FIG. 1, diamond in the form of a film or a lump can be obtained.

In FIG. 4, 31 is a microwave plasma torch;
2 is a microwave oscillator, 33 is a waveguide, and the others are the same as in FIG. In this case as well, diamond can be grown on the substrate or in the gas phase as in FIG. Note that a coaxial electrode type plasma torch can be used instead of the cavity resonator type plasma torch shown in FIG.

Example 1 Discharge of 45V-78A was carried out for 10 minutes, and approximately 9
A diamond polycrystalline film with a thickness of 4 μm was obtained on a silicon substrate of No. 03. The nozzle diameter is IM, and the pressure in the precipitation chamber is 8 Torr.
R and M were simply placed on an alumina holder, and the substrate temperature was approximately 750°C. The structure of the film was identified by X-ray diffraction and Raman scattering spectra. Uniformity of film thickness is ±
It was within 2%.

Example 2 Using the apparatus shown in FIG. 2, methane gas 20
0 ml/m, argon 12j from 3'! /m, 8
' - Flow hydrogen 86/ra, 5011z, 85V
-9OA discharge was performed for 10 minutes to obtain a 7 μm thick diamond film on the molybdenum substrate. Nozzle diameter is 31m
The deposition chamber pressure was 0.2 atm, and the substrate temperature was 920°C.

Example 3 Using the apparatus shown in Fig. 3 (substrate holder attached), 0.6 g/m alcohol vapor and argon 2 were supplied from valve 8.
1/ls mixed gas, 8' to argon 81/m, 8'
A mixed gas of 16 f/m of argon and 101/m of hydrogen was flowed, and a high frequency wave with a frequency of 4 MH2 and a vacuum tube plate power of 12 kW was used to discharge for 9 minutes to obtain a diamond film with a thickness of 18 μm on the molybdenum substrate. Nozzle diameter is 9.6f
i, Deposition chamber pressure is 0.6 atm, substrate temperature is approximately 1100°C
Met.

Example 4 Using the apparatus shown in Figure 3, 400 ml of propane was supplied from valve 8.
Mixed gas of ml/m and argon 41/m, 8' to 7
) Lt go: / 12 lim, argon 25 from 8'
C/m and hydrogen 10j! ! By flowing a mixed gas of /m and discharging at 0 kW through a vacuum tube plate cuff, approximately 1 g of diamond powder with a particle size of 150 ± 20 particles was deposited on the plate 25 in 30 minutes.
I got it. The nozzle diameter was 2 mm, the precipitation chamber pressure was 1 atm, and the discharge chamber pressure was about 3 atm.

Example 5 Using the apparatus shown in FIG. 4, methane 100
Mixed gas of ml/11 and argon 21/+, argon 31/m from 8', argon IOC/+ and hydrogen 3 from 8'
．． Flowing a mixed gas of 51/m, 2.45 GHz, 4
．． Microwave discharge at 7 kHz was performed for 10 minutes to obtain a diamond film with a thickness of 7 μm on the silicon substrate. The nozzle diameter is 3 cranes, the precipitation chamber pressure is 0.1 atm, and the substrate temperature is 890°C.
Met.

Effects of the Invention According to the method of the present invention, when synthesizing diamond using high-temperature plasma, it is not necessary to cool the substrate by water cooling, gas blowing, etc., or to cool the growth space by gas injection. It is possible to obtain a more uniform temperature distribution, thereby achieving an excellent effect of obtaining a film with uniform properties, crystals, or fine powder with uniform particle size and properties.

[Brief explanation of the drawing]

The drawings are schematic diagrams of the apparatus for carrying out the method of the present invention, in which Fig. 1 shows DC discharge, Fig. 2 shows AC discharge, Fig. 3 shows high-frequency discharge,
FIG. 4 is an embodiment of an apparatus for synthesizing diamond by generating plasma using microwave discharge. 1: DC plasma torch, 2: DC power supply, 3: Substrate, 4: Nozzle or orifice, 5: Plasma generation chamber, 5': Deposition chamber, 6: Exhaust device, 7: Gas supply device, 8.8', 81 : Valve, 11: Electric scraper, 12: AC power supply, 21: High frequency plasma torch, 22: High frequency power supply, 23: Work coil, 24:
Introducing device for solid and liquid raw materials, 25: Receiving dish, 31: Microwave plasma torch, 32: Microwave oscillator, 33: 4-wave tube. Figure 7 Figure 2 m Figure 3 Figure H

Claims (1)

[Claims] Plasma is generated by electric discharge in a single gas or a mixture of gases selected from hydrocarbon gas, hydrogen gas, and inert gas, and the gas obtained by decomposing or evaporating organic compounds or carbon materials in the plasma is adiabatically expanded. A method of synthesizing diamond using plasma, which is characterized by depositing diamond on a substrate or in a gas phase by